Gravity meter



2- I P. s. WILLIAMS 2,304,324

GRAVITY METER Filed July 27, 1939 -"ATTORNEY;I' I

Patented Dec.

UNl'lED STAT Philip s.

ES n PATENT emce- Okla aaoignor to Williams, Tulsa, Standard OilDevelopment- Company, a corporations! Delaware ApplicatlonJnly 27, 1939,Serial No. zscxur The present-invention is directed to a gravity meterand particularly to that type of gravity meter in which" the gravitymeasuring system in-' cludes a weight carried by a pivoted beamsupported by one or more springs.

One of the inherent d'ifilculties with gravity metersof the aforesaidtype, which bears a close relation to the sensitivity of the meter, isthe fact that responsiveness of the weight to changes of gravity dependupon the angle which the beam makes with the horizontal," That is tosay, the deflection of the beam from the-horizontal does not bear alinear relation to changes of gravity,

3 Claims. (01. 285-4.!)

on the fixed support 3. The metal plates carry binding posts 0. Fixed tothe beam i and suspended therefrom is a weight I which iscounterbalanced by a spring 8. ate point closer to its fulcrum is a finespring l which is used for fine adiustments. Thus far the arrangementdescribed is essentially that shown in Figure 1 of Reissue Patent No.20,137,

issued October 20, 1936, to Kenneth Hartley.

At its outer end the beam i has an extension ill in; which is mounted acoil- II which is preferably a flat coll lying in the plane of thelongiwhereby calibration of the meter is rendered difficult. Anotherdisturbing influence in meters of this type is the fact that the springor springs will not always be distorted the same amount by a given.change of gravity. but because of an effect somewhat akin to ahysteresis eifect the amount of distortion of the spring for a givenchange in gravity will often depend upon the previous position orcondition of the spring. Re-

citing a specific case, in any particular equilibrium position reading,the instrument may show 'a ysteresis effect due to the recent swing ofthe moving system from its position when clamped for transit. The effectwill be roughly proportional to the difference between theseconfigurations and thus will vary for readings at stations ofvaryinggravity values. 'lheprlncipal object of the present invention is Y theprovision of a gravity meter of the general type referred to'above inwhich means are provided to render the reading of the meter independentof the factors hitherto found objectionable. More specifically, it isthe object of the present invention to Provide a null point readinggravity meter-in which changes of gravity are measured as electricalvalues which in turn are made dependent upon a force necessary torestore the moving system of the gravity meter, after deflection bygravity, to its null position.

The present invention will be more fullyunderstood from the followingdetalleddescription of the accompanying drawing in-which the singlefigure is a perspective view, indiasrammatic tudinal axis of beam i andvertically arranged. This. coil is connected to binding posts it carriedby the metal strips 2. The coil is arranged in the field of a pair ofpermanent magnets II which are secured to the frame work of the gravitymeter with pole faces parallel with the .plane of the coil. One of thepole pieces is provided with a mark it and the coil carries a pointer iswhich is adapted to coincide with the'mark when the beam is in its nullposition. An optical system, including a triangular prism it and lensesit, 18 and i9, is focused on the mark It.

Attached to the binding posts 8 are the ter-,

minals of a circuit including a reversing switch 20, a meter II, abattery 22 and an adjustable resistance 23. The switch 2! is provided sothat current may be sent through the coil in either direction.

' In using the system descrbed above, the gravity meter is set up at abase station and the current from battery 22 is adjusted by resistance23 so form, of one embodiment of the present invenf tion as applied to aconventional type of gravity to the drawing in detail, numeral Idedgnatesabeamoflnsulatingmaterlalhaving filxed to each of its sides astrip of conducting materiall. 'I'heinner endofthebeamlshinged to a l-byspring hinges 4 connectin: the aforesaid metal strips 2 to metal platesI as to bring the pointer ii in coincidence with taken as a directfunction-of the diflerencein gravity between the two stations.

In practice it is preferred that the magnets be of the permanent typealthough electrical magnets may be employed. It is also preferred tomake the distance from the cell through the ful-- crum as. largev aspossible since the small null setting force preferred for a givengravitational pull will be inversely p oportional .to this distance.

Also fixed to the beam.

- The reversibility of the deflecting force by reversing the current,together with the consequent fact that the system works around a stateof zero force, contributes to the accuracy of the measurements. That is,a gravity range of say 1000 units,

tem in the same position for all readings since' consequently the springtensions are always the same. Furthermore, the reading position can bemade closeto the clamped position or, for certain constructions,coincident with it. The calibration of the instrument is taken out ofthe domain of the gravity meter proper and made to depend on electricaland magnetic arrangements', and the runctioning oi the latter is wellunderstood and controllable. The only requirement on the meter proper isthat the equilibrium position of the moving system, other things beingnull point by an electrical means. This can easily be done by arrangingan electrical circuit which is closed when the beam is in itsnllll pointin a manner already known,

Many possible configurations of coil and magnetic structure will occurto those skilled in the art. Such modifications are contemplated withinthe scope of the present invention which is not limited to the specificembodiment shown, but is defined in the appended claims in which it isintended to claim the invention as broadly as the prior art permits.

What is claimed is: 1. In a gravity meter having a pivoted beam carryinga weight responsive to gravity changes,

in combination, a flat coil carried by a free end of said beam andarranged in the plane of movement of said beam, a pair of pole piecesmounted on. either side of said coil with their faces parallel with theplane of said coil, a source of ourrent connected to said coil and meansfor indi-v constant, change sufliciently with changes in gravitationalpull so that the optical, or other observational error, in setting thesystem to the null position will represent a negligible error in thecorresponding gravity value. In fact, most of the elements on which thecalibration "will depend can be physically separate from the gravitymeter proper and hence be readily accessible for check or adjustment. Itwill also be noted that the spatial uniformity of the magnetic fieldbetween the pole pieces cannot affect the linearity of the reading sincethe coil is in the same position relative to the magnetic structure forall readings.

The improvement of the present invention makes the gravity meter readilyadaptable to remote reading. when this is desired, it is necessarytoreplace the optical means for observing eating the amount of currentsupplied to said coil;

2. A combination according to the preceding claim in which one of saidpoles carries a mark indicating the null position of the beam andthecoil carries a pointer adapted to cooperate with said mark toindicate the null position of said beam.

3. In a gravity meter having a pivoted beam carrying a weight responsiveto gravity changes and provided with a system of springs attached tosaid beam to oppose said weight, in combination, a fiat coil carried bya free end of said beamand arranged in the plane ofmovement of saidbeam, 2. pair of pole pieces mounted on either side of the coil withtheir faces parallel with the plane of said coil, a source of directcurrent connected to said coil by an electric circuit including meansfor regulating and indicating the amount of current supplied to saidcoil, and means for reversing the direction of now of current in saidcoil. 4 I

PHILIP S. WILLIAMS.

